The present invention relates generally to an electrophotographic printing machine and, more particularly, to a compact apparatus for feeding copy media sheets into an image transfer zone and for receiving copy sheets from a fusing area.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charge thereon in the irradiated areas resulting in the formation of an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet, which is fed from a copy sheet input section. The toner particles are heated to permanently affix the powder image to the copy sheet. The copy sheets are then delivered to a copy sheet output station where they may be simply stacked or where further operations, such as collating, stitching, or stapling may be performed.
Commercial machine architecture, as exemplified by the machines disclosed in U.S. Pat. Nos. 4,746,111 and 4,221,379, utilize a first input station to store the copy paper and feed the individual sheets into the transfer area and a second copy sheet output station on the opposite side of the machine to receive the copy sheets bearing the transferred and fused images. These two patents are typical of the "in-line" left to right or right to left copy sheet flow. The copy sheet flow may also be "folded" where the copy sheets are returned to the same side of the machine, albeit at a different location. Such a system is shown in U.S. Pat. No. 4,942,435. For either case the copy sheet input station generally incorporates a copy sheet feed tray or the like while the copy sheet output station generally incorporates a stacker tray/sorter or the like. Each station has the common characteristic of encompassing an operational space which is only partially filled by copy sheets, the remainder of the space being vacant. For example, the total volume encompassed by a copy sheet input tray may be completely filled with sheets at full loading but as the sheet feeding operation progresses, the space occupied by the sheets progressively lessens until the sheets are completely fed out leaving an empty air space. An analogous situation is present at the copy sheet stacker tray which is empty at the start of a copy operation and which gradually fills during operation.
It will be appreciated that the copy sheet input and output stations are, from an architectural viewpoint, not optimally designed. Since the unit manufacturing cost of commercial reprographic machines is substantially influenced by the size of the machine stations, it would be advantageous to make the copy sheet input and output stations as compact as possible. It would also be desired to optimize the efficiency of the folded type of architecture. According to the present invention, these objects are realized by incorporating the input and output stations into one compact apparatus which combines both functions. The novel apparatus has a total volume which is filled with a combination of input copy sheets waiting to be fed into the transfer area of the copier and with copy sheets outputted from the fusing station. This concept is enabled by providing a variable boundary between the input and output stations. In a preferred embodiment, the variable boundary coincides with the bottom of a copy sheet stacker tray which moves in a vertical direction to advance into the area vacated by the copy sheets after they are fed out of the copy sheet supply tray. More particularly, the invention relates to an improved electrophotographic printing machine of the type in which a latent image is developed on a photoconductive member and a developed image transferred to a copy sheet and the developed image fixed at a fusing station, with successive copy sheets being supplied to said transfer station from a sheet loading station and exiting said fuser station into a sheet stacking station, whereby the improvement includes: a first, fixed surface for supporting the copy sheets being supplied to said transfer station and a second, variable surface overlying said fixed surface, said second surface being vertically movable.